The Colorimetric Test for Organic Impurities

The colorimetric test is a reliable indicator of the presence of harmful organic matter except in areas where there are deposits of lignite. To make this test, an ordinary 12-oz. prescription bottle is filled to the 4^-oz. mark with a sample of the sand. To this is added a 3 per cent solution of caustic soda1 (sodium hydroxide) until the 7-oz. mark is reached. The contents are thoroughly shaken and then allowed to stand for 24 hr.

At the end of this time the color of the liquid will indicate whether the sand contains dangerous amounts of organic matter. A clear liquid indicates absence of organic matter. A straw-colored solution indicates some organic matter, but not sufficient to be seriously objectionable. Darker colors indicate that the sand contains injurious amounts and should not be used without washing. After washing a retest should be made to see if it is then satisfactory.

1 A 3 per cent solution of caustic soda is made by dissolving 1 oz. of sodium hydroxide in 1 qfc. of water, preferably distilled. Sodium hydroxide may be purchased at any drug store at nominal coat. The solution should be kept in a glas? bottle tightly stoppered. Handling sodium hydroxide with moist hands may result in serious burns. Care should be taken not to apill the solution, which is highly injurious to clothing, leather, and most other materials.

If preferred, the testing solution may be made by dissolving a heaping tcaspoonful o£ lye in 14 pt. of clear water. Any household lye that contains as much as 94 per cent sodium hydroxide may be used.

Fig. 282.—If a 2-in. sample of sand contains more than in. of siJt, the sand should be washed or rejected.

Fro. 283 —Tho colorimetric test id used to detect the presence of harmful amounts of organic matter in aggregate». A clear liquid as shown in the bottle on the left indicates that the aggregate is free from organic matter. The slightly colored liquid in the center bottle indicates the presence of some organic matter but not enough to prove injurious. The dark liquid in the right-hand bottle shows that the aggregate is unsatisfactory for concrete work unless the organic matter is washed out.

343. Washing Aggregates.—Sand or pebbles containing injurious amounts of silt or organic matter should be washed. A simple washing device is shown in Fig. 284. The materials to be washed are piled on the

Fine mesh screen \ wrih 50 meshes to ~ a linear inch

Plart of screen showing cleats

C/eaf

1x6'rough boards \

Fine mesh screen \ wrih 50 meshes to ~ a linear inch

Fig. 284.—Design for a simple device for wash in r aggregates.

Fig. 284.—Design for a simple device for wash in r aggregates.

higher end. Water is applied by means of a garden hose, pail, or other convenient method. As the materials are washed down the incline, silt,

Dimensions for Ik>rromless Maas dring Boxks op Various Capacities

dust, and organic matter separate out and are carried away in the water. It is a good plan to rim check tests to see whether washing has been thoroughly done.

344. Water.—Water used to mix concrete should be clean and free from oil, alkali, and acid. In general, water that, is fit to drink is good for concrete.

345. Measure All Materials Accurately.—All materials, particularly water, should be accurately measured. A pail marked on the inside to indicate gallons and quarts is handy for measuring mixing water. Aggregates can easily be measured by using a box or bottomless frame made to hold exactly I cu. ft., 2 cu. ft., or any other volume desired (see Fig. 285). To measure the materials, the frame is placed on the mixing platform and filled. When the'required amount of material has been placed in it, it is lifted, and the material remains on the platform. In mixing one-sack batches, it is not necessary to provide a measure for cement as one sack holds one cubic foot. A pail may also be used in proportioning materials. For example, a 1-2^-3 batch of concrete would be measured by taking 1 pail of Portland cement, 2% pails of sand, and 3 pails of pebbles or stone.

346. Mixing the Materials.—Concrete may be mixed either by machine or by hand. Machine mixing is preferred. It is recommended that the mixer be run for at least 2 mill, after all materials, including water, are placed in the mixer drum. First-class concrete can be mixed by hand. Whichever way mixing is done, it should continue until every pebble or stone is completely coated with a thoroughly mixed mortar of sand and cement.

A tight barn floor or some paved area like a feeding floor provides a satisfactory surface on which to mix concrete by hand. If such floors are not available, a watertight mixing platform at least 7 ft. wide and 12 ft. long should be made. A platform of this size is large enough for two men

using shovels to work upon at one time. Such a platform should be made of matched lumber so that joints will be tight. Strips should be nailed along three sides of the platform to prevent materials from being washed or shoveled off while mixing.

The usual procedure in mixing concrete by hand is as follows: The measured quantity of sand is spread out evenly on the platform. On this the required amount of cement is dumped and evenly distributed. The cement and sand are then turned over thoroughly with square-pointed shovels enough times to produce a mass of uniform color, free from streaks of brown and gray. Such streaks indicate that the sand and cement have not been thoroughly mixed. The required quantity of pebbles or broken stone is then measured and spread in a layer on top of the cement-sand mixture, and all of the materials again mixed by turning with shovels until the pebbles have been uniformly distributed. At least three turnings are necessary. A depression or hollow Is then formed in the center of the pile and the correct amount of water added slowly while the materials are turned with square-pointed shovels, this turning being continued until the cement, sand, and pebbles have been thoroughly and uniformly combined,

347. Placing Concrete.—Concrete should be placed in the forms as soon as possible, in no case more than 45 min. after mixing. It should be deposited in layers of uniform depth, usually not exceeding 6 in. When placed in the forms it should be tamped and spaded so as to cause it to settle thoroughly everywhere in the forms and produce a dense mass. By "spading" is meant the working of a spade or chisel-edged board in the concrete and between it and the side of the forms, moving the spading tool to and fro and up and down.

This working of the concrete next to the forms forces the large pebbles or stone particles away from the forms into the mass of the concrete, and insures an even, dense surface when forms are removed.

34.8. Finishing Concrete.—The surface of walks, and floors in barns, hog houses, and most other farm buildings, should be finished with a wood float to give a smooth, yet gritty, nonskid surface. A steel trowel should be used sparingly, if at all, as its use is likely to result in an oversmooth surface that will be slippery when wet.

Where a smooth surface is desired, however, as in a poultry house floor, most of the smoothing is done with the wood float, and, after the concrete has stiffened somewhat, the final finishing is done with a steel trowel. The steel trowel should be used sparingly and only in the final finishing, since excessive trowelling draws the fine material to the surface, which may cause hair checking and dusting after hardening.

349. Protecting Newly Placed Concrete; Curing.—Do not permit the newly placed concrete to dry out. Protect it from sun and drying winds for 1 week or 10 days; otherwise the water necessary for the proper hardening will evaporate, resulting in a loss of strength. Floors, walks, and similar surfaces can be protected by covering with moist earth, or hay or straw as soon as the concrete has hardened sufficiently so that the surface will not be injured. This covering should remain on for 1 week or 10 days and be kept moist by occasional sprinkling.

Walls or other sections that cannot conveniently be covered in the mariner suggested can be protected by hanging moist canvas or burlap

over them and wetting down the work often enough to keep it moist for 10 days after placing. In cold weather, work should be protected by a layer of straw, but need not be kept moist, as evaporation is riot rapid.

350. Forms.—Forms, generally made of wood, hold the concrete in place until it hardens. Rough lumber may be used where appearance is not important, but where a smooth finish is desired, the forms should be carefully built of good planed lumber, Tongue-and-grooved lumber or shiplap is commonly used to give tight joints. Forms should be built so they can be easily removed without damage to the fresh concrete and with the least possible damage to the form lumber. Where forms are to be used again, they may be built in sections to facilitate removal. It is important that forms be built tight and strong and that they be well-

braced in position to prevent bulging when the wet concrete is tamped into place. Wood forms are commonly oiled with crude oil or crankcase draining« to prevent warping and to prevent concrete from sticking to them.

For foundation work below ground, forms are not necessary if the sides of the excavation will stand without caving.

Fig. 2S7.—Forms for foundation walls above grade. Concrete may bo pUoed directly into the earth trench below grade if care is taken to keep the side wail» firm and straight.

351. Removal of Forms.—Forms should not be removed until the concrete has hardened sufficiently to be self-supporting and until there is no danger of damage to the concrete in removing the forms. The time required will vary from 1 day to 2 weeks or more, depending upon the weather, the nature of the work, etc. In summer, wall forms may generally be removed after 1 or 2 days, and In colder weather in from 4 to 7 days. Forms for roofs and floors over basements should not be removed in less than 7 days in summer and 14 days in colder weather.

352. Reinforcing Concrete.—Concrete, like stone, is strong in compression. It can support very heavy loads that tend to mash or erush it. Steel rods or other forms of reinforcing should be used in concrete," however, where loads or forces tend to pull it apart. It is important that the reinforcement be placed where it will do the most good in helping the concrete to resist the stretching or pulling forces. For example, in a concrete lintel or beam, the reinforcement should be placed near the lower side, as that is the side that tends to stretch or pull apart when the beam

Fig. 2S7.—Forms for foundation walls above grade. Concrete may bo pUoed directly into the earth trench below grade if care is taken to keep the side wail» firm and straight.

is loaded. Important or elaborate structures, as floors above ground, beams, columns, and retaining walls, should be designed by an experienced engineer.

Fig. 258.—Forma for sidewalks usually consist of two by fours set on edge. Theso serve as guide« in striking off the surface. For convenience, sidewalks are generally built in sections.

363. Concrete Work in Cold Weather.—Concrete can be made during cold weather if a few simple precautions are observed. In early winter, when freezing occurs only at night, it is necessary merely to protect the concrete after it has been placcd in the forms. As the weather grows colder and freezing temperatures prevail, the mixing water and aggregate should be heated and the work protected after it is poured by covering with straw, manure, paper, or canvas, or by building enclosures around the new work and heating with stoves. Aggregate may be heated by building a fire inside an old smokestack, metal culvert, or steel barrel laid on its side, and piling the aggregate over it. Cement should not be heated, nor should water hotter than 150°F. be mixed with the cement.

Fio. 290.—Forma for building a stock watering tank, platform, and b?u*e.

354. Mortar for Masonry Walls.—Portland cement mortar is recommended for laying concrete blocks, building tiles, rocks, or bricks. For ordinary work a mortar composed of 1 part of cement, 1 part of hydrated lime or well-slaked lime, and not more than 6 parts of clean well-graded sand, all measured by volume, is considered satisfactory.

Where extra strength and density are desired, as in building water storage tanks, silos, and similar structures, a mortar consisting of 1 sack of cement, 3 cu. ft. of sand, and 10 lb. of lime, is recommended.

Mortar should be mixed thoroughly with just enough water to give the desired plasticity and workability. Thorough mixing improves the plasticity of mortar, and less mixing water is required to obtain a workable consistency when the time of mixing is increased. The lime is used in mortar to make it more plastic or "fat."

355. Quantities of Materials Required.—The amounts of cement and aggregate required for a given job majr be closely figured by first determining the total volume of concrete required and then referring to a table such as Table VII or VIII.

1 Quantities may vary 10 per oeat either way, depending upon character of aggregate used.

1 Quantities may vary 10 per oeat either way, depending upon character of aggregate used.

Table VIII.—Materials Required for 100 Sq. Ft. of Surface roa Varying

Thicknesses of Concrete or Mortar1

Thickness of mortar or concrete, in.

Amount of mortar or concrete, cu. yd.

Proportions

1-2

1-3

1-1-1%

Cement, sacks

Fine aggregate, cu. ft.

Coarse aggregate, cu. ft.

Cement, sacks

Fine aggregate, cu. ft.

Coarse Hggrc-ga tef cu. ft.

Cement, sacks

Fine aggregate, cu. ft.

Coarse aggregate, cu. ft.

0.15

0.23

0.31

0.38

0.46

0.64

0 62

0.92 1.24 1.56 1.85 2.46 3.08 3.70

4.5 5.4 6.4 7.3

2.8 3.6 5.4 7.4 9.0 10.8 12.8 14.6

14.1

»... » • » m » " r •

6.2

6.2

3.9 5.3 6.5 7.8 9.2 10.5

1-134-2

1-2M-3

17.3

5.8 7.8 9.8 11.5 15.4 19.3 23.1

12.9

17.3

23.6 29.6 35.2 46.8 58.5 70.4

12.3

15.4

49.3 61.6 74.0

* Quantities may vary 10 per cent either way, depericing upon character of mregiU uacd.

* Quantities may vary 10 per cent either way, depericing upon character of mregiU uacd.

The required quantities of materials may also be estimated by using the following formula:

c + s + g where C = the number of sacks of cement to make a cubic yard of concrete.

c — 1, or the proportions of cement in the mixture.

8 = the proportions of sand in the mixture.

g = the proportions of gravel or coarse aggregate in the mixture. For example, suppose it is desired to know the materials required to make 1 cu. yd. of concrete (27 cu. ft.) with a 1-2)4-3 mixture. Substituting in the formula,

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